Thomas A. Weaver

Galacti chemical evolution: Hygrogen through zinc

Using the output from a grid of 60 Type II supernova models (Woosley & Weaver 1995) of varying mass (11 approx. less than (M/solar mass) approx. less than 40) and metallicity (0, 10(exp -4), 0.01, and 1 solar metallicity), the chemical evolution of 76 stable isotopes, from hydrogen to zinc, is calculated. The chemical evolution calculation employs a simple dynamical model for the Galaxy (infall with a 4 Gyr e-folding timescale onto a exponential dsk and 1/r(exp 2) bulge), and standard evolution parameters, such as a Salpeter initial mass function and a quadratic Schmidt star formation rate. The theoretical results are compared in detail with observed stellar abundances in stars with metallicities in the range -3.0 approx. less than (Fe/H) approx. less than 0.0 dex. While our discussion focuses on the solar neighborhood where there are the most observations, the supernova rates, an intrinsically Galactic quality, are also discussed.

The evolution of massive stars including mass loss - Presupernova models and explosion

The evolution of massive stars of 35, 40, 60, and 85 solar masses is followed through all stages of nuclear burning to the point of Fe core collapse. Critical nuclear reaction and mass-loss rates are varied. Efficient mass loss during the Wolf-Rayet (WR) stage is likely to lead to final masses as small as 4 solar masses. For a reasonable parameterization of the mass loss, there may be convergence of all WR stars, both single and in binaries, to a narrow band of small final masses. Our representative model, a 4.25 solar-mass WR presupernova derived from a 60 solar mass star, is followed through a simulated explosion, and its explosive nucleosynthesis and light curve are determined. Its properties are similar to those observed in Type Ib supernovae. The effects of the initial mass and mass loss on the presupernova structure of small mass WR models is also explored. Important properties of the presupernova star and its explosion can only be obtained by following the complete evolution starting on the main sequence.

Nucleosynthesis in massive stars and the 12C(α, γ)16O reaction rate

Abstract The evolution of a grid massive stars ranging from 12 to 40 M⊙ has been followed through all stages of nuclear burning up to the point of iron core collapse. The critical and highly uncertain rate for the reaction 12C(α, γ)16O has been varied over a range from 0.5 to 3.0 times that given by Caughlan and Fowler and two different prescriptions for semiconvection have been explored. The nucleosynthesis resulting from integrating the yields of these models over plausible initial stellar mass distributions is found to be in excellent agreement with the observed solar abundances of virtually all the intermediate mass isotopes (16 ≤ A ≤ 32) if, and only if, the rate of the 12C(α, γ)16O reaction is taken to be 1.7 ± 0.5 times that given by Caughlan and Fowler. This range is a small subset of what is allowed by current experimental measurements and can be taken as a nucleosynthetic “prediction” of the value that this rate needs to have in order to prevent 5- to 100-fold deviations from the observed relative abundances of key isotopes. These results are insensitive to the assumed slope of the initial stellar mass distribution within observational limits, and relatively insensitive to the theory of semiconvection (except for the apparent excessive production of 18O when semiconvective mixing is suppressed). Three of the stars have been followed through simulated explosions to obtain the explosive modifications to their nucleosynthesis (including the “neutrino process”), which for most isotopes is relatively small. Isotopic yields of both stable radioactive products are tabulated as are the calculated iron core masses of the presupernova stars.

26Al and 60Fe from Supernova Explosions

Using recently calculated yields for Type II supernovae, along with models for chemical evolution and the distribution of mass in the interstellar medium, the current abundances and spatial distributions of two key gamma-ray radioactivities,

EVOLUTION AND EXPLOSION OF MASSIVE STARS

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Successive X-ray bursts from accreting neutron stars

Al and

The Reaction Rate Sensitivity of Nucleosynthesis in Type II Supernovae

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Nucleosynthesis below A = 100 in Massive Stars

Fe, are determined. The estimated steady state production rates are 2.0

Presupernova models: Sensitivity to convective algorithm and coulomb corrections

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The physics of supernovae

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